This Recommendation specifies a methodology for describing equipment for transport networks based on the transport processing functions and architectural entities defined in [ITU-T G.805]. It defines the set of generic atomic and compound functions and the set of rules for how to combine them. The detailed characteristics of equipment functional blocks of specific transport networks (e.g., SDH, OTN) will be defined in follow-up Recommendations based on this methodology. Equipment can then be described by an equipment functional specification (EFS) which lists the atomic functions and their interconnection.

In addition, generic functionality, processes and overall performance objectives for transport networks are defined in this Recommendation.

The internal structure of the implementation of this functionality (equipment design) need not be identical to the structure of the functional model, as long as all the details of the externally observable behaviour comply with the EFS.

Equipment which is normally stated to be compliant with this Recommendation may not fulfil all the requirements in the case that it is interworking with old equipment that is not compliant with this Recommendation.